This invention relates to an information detecting system of scanning type using an optical integrated circuit of waveguide type, and more particularly to an information detecting system of the type described above which is suitable to reduce the size and improve the accuracy of alignment of, for example, an alignment optical system for use in a semiconductor manufacturing apparatus.
Discrete parts including lenses, mirrors and prisms were used to constitute prior art optical systems such as an pickup for a compact disk and an alignment optical system for use in a semiconductor wafer exposure apparatus commonly called a stepper. Because of such a construction, not only difficulty was encountered for reducing the size and weight of the prior art alignment optical system, but also complex system adjustment was required during assembling the prior art optical system. Thus, the prior art optical system had the problem of high costs.
An optical integrated circuit of waveguide type has been proposed as a means for solving the problem pointed out above. FIG. 1 shows an optical integration circuit of waveguide type similar to that shown in FIG. 1 at page 40 of "AN INTEGRATED-OPTIC DISK PICKUP DEVICE", the Technical Research and Study Report OQE85-72 (1985) reported in The Institute of Electronics and Communication Engineers of Japan. This report refers to application of such an optical integration circuit to a pickup for an optical disk such as a compact disk or an optical disk memory. Referring to FIG. 1, a laser beam emitted from a semiconductor laser 1 is guided toward a waveguide layer 3 in the form of a thin film of a dielectric material formed on a substrate 2. A beam splitter 4 and a focusing grating coupler 5 constituted by a diffraction grating are provided on the waveguide layer 3 so as to focus the laser beam, and the focused laser beam 6 forms a team spot 8 on an optical disk 7. The laser beam 6 modulated by signal pits 9 formed on the optical disk 7 passes through the focusing grating coupler 5 and the beam splitter 4 again and after being split into halves, reaches a photodetector 10 composed of four elements. Electrical output signals appear from the four elements of the photodetector 10, and, on the basis of these electrical signals, tracking and focusing errors are detected together with information obtained from the signal pits 9.
In the form of the optical integrated circuit of waveguide type shown in FIG. 1, the passive optical elements such as the lens and the beam splitter are built in the substrate. However, a beam deflecting function using a SAW (surface acoustic wave) device which is an active optical element can also be added to the optical integrated circuit of waveguide type shown in FIG. 1. Such an optical integrated circuit is described, for example, at pages 179-180 of "Optical Integrated Circuits" edited by the members in The Meeting of Optical Engineers of the Japan Society of Applied Physics, 1988. FIG. 2 shows an optical integrated circuit of waveguide type similar to that described in the above publication. Referring to FIG. 2, titanium (Ti) is diffused in the surface of a substrate 2 of lithium niobate (LiN.sub.b O.sub.3) to form an optical waveguide layer 3, and a SAW electrode 11 of a material such as aluminum (Al) is formed on the optical waveguide layer 3. When a high-frequency a.c. signal 12 is applied to this SAW electrode 11, the SAW electrode 11 is excited to generate surface acoustic wave (SAW) 13. At this time, so-called acoustic Bragg diffraction of an incident laser beam 14 is caused by the function of a diffraction grating having periodically changing film thickness and index of refraction, and the incident laser beam 14 is split into a beam of zero-th order 15 and a diffracted beam of first order 16. By changing the frequency of a high-frequency a.c. signal 12, the angle between the zero-th order beam 15 and the first order diffracted beam 16 is changed, so that the beam deflecting function is exhibited.
An example of application of such an optical integrated circuit of waveguide type to an optical disk is described at pages 13-14 of "Micro-Optics News," Vol. 6, No. 3 (1988) edited by The Japan Society of Applied Physics. This application intends to shorten the tracking access time for the optical disk by the SAW type beam deflecting device.
These optical integrated circuits of waveguide type described hereinbefore are manufactured by a process substantially similar to the known process for manufacturing various semiconductor devices, and the process includes the steps of exposure-development, etching and diffusion. Therefore, the optical integrated circuit of waveguide type having a high degree of dimensional accuracy can be fabricated in a similar manner to the fabrication of the semiconductor devices without requiring any assembling adjustment, and the optical system thus realized has a reduced size and weight and can stably operate.
JP-A-59-74625 discloses a method for scanning or diffracting a laser beam by a galvanomirror thereby detecting a diffracted beam pattern on a semiconductor wafer.